Solar Water Heater

ABSTRACT

A low-cost absorber panel for a solar hot water heating system is provided. An aluminum absorber plate, under exposure to solar radiation, makes an efficient transfer of heat to water circulating within the collector panel by direct contact with the medium in an optimized area-to-volume configuration. An innovative use of fasteners makes it possible to accommodate expansion for freezing and to allow for disassembly and maintenance. Additionally, a low-cost heat exchanger and a low-cost solar hot water system are presented using common structures.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a Continuation-in-Part of U.S. patent application Ser. No.12/335,577, filed Dec. 16, 2008, and to which priority is hereinclaimed.

FIELD OF THE INVENTION

The invention relates to solar energy collectors, and more specificallyto low pressure solar hot water heater absorbers.

BACKGROUND OF THE INVENTION

With the potential of future capacity shortages in the aginginfrastructure of the electricity grid in the United States, not tomention the adverse-weather-prone supply of natural gas in the nation,solar energy represents an alternative to looming energy crisis's, aswell as rising energy costs in the present. Next to space heating, waterheating is the most significant factor in residential energy consumptionand accounts for 13% of the household energy bill. What is needed is asolar hot water heating installation that can be accomplished on abudget by the average homeowner.

Flat-plate solar collectors for water heating are present in the art.They are comprised of a heat-absorption panel in contact withcirculating water and are typically housed under a transparent coveringand over an insulating bed. The solar collectors are part of a systemincluding a water supply and/or storage means, a circulation pump, and aheat-exchanger means. The heat transfer efficiency is a function ofreflective, conductive, and convective heat losses, as well as thetemperature differential between the absorption panel and the incidentwater. The convective losses are affected by the insulating bed and airenvelopes, and the reflective losses depend on the reflectivity offacing surfaces, including the transparent covering.

Commercially available types of flat-plate collectors are typicallyconstructed with rows of copper riser tubes with attached copper finsexposed to radiant heat from the sun. Circulation of water through thetubing requires a pressure gradient, which is proportional to thecross-section of the tubing for a specified rate of flow. The pressureplaces stress on seals and soldered joints. Since the water is not indirect contact with the collector plate, some loss of conductive heatefficiency occurs.

A preferred type of collector would be a low pressure system wherein thewater circulates through relatively wide passageways betweenthinly-sandwiched absorber and companion plates and wherein the water isin direct contact with the absorber plate. This is thermally moreefficient in two ways: Firstly, the water is intimate with the radiantlyheated surface of the absorber plate, so conductive losses are less; andsecondly, the absorber plate operates with a lower thermal gradient withrespect to the environment, so convective losses are less. Thepassageways are sufficiently broad as to allow a 1.5 psi pressure for a2 gpm circulation; consequently, seal integrity is less of a problem.There should be a serpentine path of water flow created by internalbaffles which lengthen the contact time and create a certain amount ofturbulence for the even distribution of heat. The present inventionaddresses a simple means for constructing such a system fromreadily-available materials, and costs less on a per BTU basis than thecopper-tube version mentioned above.

The prior art discloses different methods of construction for lowpressure collectors. U.S. Pat. No. 4,103,675 to Bar-On, for example,uses an assembly of extrusions with channels therein to form passagewaysbetween inlet and outlet manifolds. The passageways do not follow atortuous path in this case. Insufficient dwell time in contact with aradiantly heated surface might be a problem with this construction,which problem is overcome by the preferred serpentine path. Such aconstruction, additionally, involving welded joints, cannot be takenapart for cleaning and maintenance. Furthermore, the welding of metalparts, and particularly aluminum parts, is not a fabrication process incommon usage in the home.

Another method is exemplified by U.S. Pat. No. 4,182,308 to Reynolds.Reynolds teaches a construction wherein two sheets of rubber-likematerial are bonded along the periphery to create a water-tight interiorand in alternating parallel strips with unbonded portions at the ends tocreate a serpentine flow path. Channels are formed by expansion of thematerial between the bonds when water is introduced to the system.Again, the bonded construction makes disassembly impossible, and thethermal efficiency of the elastic material is furthermore sub-optimal.Rubber, for example, has a thermal conductivity of 1.6 W/m-K, whereasthe thermal conductivity of aluminum, by comparison, is 237.

U.S. Pat. No. 4,315,499 to Shonerd demonstrates a third alternative forchannel construction. Shonerd discloses baffles formed as a part of abase extending from sidewalls to create the flow path which alternatesfrom one sidewall to the other. The sidewalls and the baffles are thespacers which form the narrow-depth passageways. While Shonerd uses athermally conductive metal absorber plate over the base, and while thesystem is conceptually capable of disassembly, Shonerd's construction,on the other hand, does not use simplified materials readily availableto the average homeowner.

Weideman, in U.S. Pat. No. 4,170,223, teaches a solar collector panelhaving end caps which form a seal with a gasket at the periphery. Incontrast to such methods as welding, soldering, or bonding, the end capspresent what would appear, at first, to be a simplified means ofassembling a sandwich construction of two plates. The end caps require,however, additional structure to prevent them from dislodging. Thesimplicity of method is undone by the complication of structure.Weidemen, furthermore, does not teach channeling to circulate water in aserpentine path.

What is missing in the prior art is a simplified structure for a solarcollector which is thermally-efficient, easily-maintainable, easy tofabricate, and easily convertible to a heat exchanger in a dual-userole. The key is to plan the solar collector for low-pressure operation,where the requirements for sealing are relaxed, where the physicalproperties of materials are not particularly critical, and where methodscan be as simple as hand-tightening, for example.

BRIEF SUMMARY OF THE INVENTION

In view of the above-mentioned unfulfilled needs, the present inventionembodies, but is not limited by, the following objects and advantages:

A first objective of the present invention is to achieve a reducedinstallation cost.

A second objective of the present invention is to achieve an operatingpressure not exceeding 2.5 psi, and preferably, not exceeding 1.5 psi,for a circulation flow of 1.5-2.0 gpm.

A third objective of the present invention is to provide an absorberplate material optimizing thermal efficiency with cost.

A fourth objective of the present invention is to provide an absorberplate with a thermal conductivity exceeding that of stainless steel at16.3 W/m-K.

A fifth objective of the present invention is to provide a means forcreating spacing and sealing between collector plates which is simple toconstruct with readily available materials.

A sixth objective of the present invention is to provide a means forcreating channeling and flow paths which is simple to construct withreadily available materials.

A seventh objective of the present invention is to provide a means fordisassembling and cleaning the solar collector for easy maintenance.

An eighth objective of the present invention is to provide a water-tightmeans for sealing having an integrated means for securely, butremovably, binding the plate components into a composite.

A ninth objective of the present invention is to eliminate the need foran expansion tank by providing a means for expansion to accommodatechanging temperatures.

A tenth objective of the present invention is to provide an apparatususable as either an absorber panel or a heat exchanger.

An eleventh objective of the present invention is to provide a solar hotwater system using common architecture.

These and other objects of the invention to become apparent hereinafterin accordance with the invention are realized in a low-pressure absorberpanel for solar hot water systems comprised of a rectangular aluminumabsorber plate combined with a matching aluminum companion plate in asandwich-like composite. The two plates are held together with a meansfor binding. A means for spacing is inserted between the plates to forma boundary there around and create a water-tight internal space for aflow of water there through. Included in the internal space is a meansfor channeling defining a serpentine flow path. The water enters theinternal space through a port in one of the absorber and companionplates and exits through another port in one of the absorber andcompanion plates, the two ports located so as to maximize the serpentineflow path. The water entering the internal space and moving therethrough under low-pressure is heated by contact with the absorber plate,which is exposed to solar radiation. The water exits the space totransfer the heat to an external system.

In a preferred embodiment, the means for spacing is an elastic gasket ofsubstantially rectangular cross-section which is arrayed along theperiphery edges of the absorber and companion plates and tensioned toprovide a compression seal.

In another aspect of the preferred embodiment, the means for binding isan extruded clip having arms angled so as to form a narrowed opening,the extruded clip covering the elastic gasket of substantiallyrectangular cross-section along the length of each periphery edge, theelastic gasket compressed between the arms to form a wedge shape whichresists removal of the extruded clip from the periphery edge.

In still another aspect of the preferred embodiment, the means forchanneling is a plurality of elastic strips of substantially rectangularcross-section. The elastic strips extend in alternation from one end orthe other of the gasket at the periphery, beginning with the end closestto the entry port and ending with the end closest to the exit port, to apoint short of the opposite end. The parallel channels formed therebyare connected to adjacent channels by alternating passages. The elasticstrips are held in place and in compression by bolts and nuts sealedwith o-rings spaced along the length thereof.

In an alternative embodiment of the present invention, the means forspacing is an elastic gasket of substantially circular cross-sectionwhich is arrayed along the periphery edges of the absorber and companionplates and adjustably tensioned to provide a compression seal. In thesame embodiment, the means for binding is machine screws and nutsstraddling the gasket of substantially circular cross-section along theextent thereof, the machine screws optionally provided with o-ring sealsfor positioning in the internal space.

In another alternate embodiment, a low-pressure heat exchanger iscomprised of essentially the same structural elements as thelow-pressure absorber panel. In the heat exchanger case, heated water iscirculated to exchange heat through both the absorber and the companionplates to a host medium.

In yet another alternative embodiment, a solar hot water system iscomprised of at least one absorber panel and at least one heat exchangerconfigured as discussed above. The absorber panel and heat exchanger areconnected by a means for circular fluid communication and a means forcreating a circulation current to transfer radiant solar heat from theabsorber panel to convective heat from the heat exchanger inside aheat-exchange vessel filled with water.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

Various other objects, features and attendant advantages of the presentinvention will become fully appreciated as the same becomes betterunderstood through the accompanying drawings, in which like referencecharacters designate the same or similar parts throughout the severalviews, and wherein:

FIG. 1 is a perspective view of the assembled solar hot water heater;

FIG. 2 is an exploded perspective view of the solar hot water heater;

FIG. 3 is a perspective view of the absorber panel;

FIG. 4 is a perspective view of the absorber panel with the absorberplate removed;

FIG. 5 is a partial sectional view of the absorber panel showing thegasketing and channel;

FIG. 6 is a partial cutaway plan view showing fastener and o-ringdetails;

FIG. 7 is a partial sectional view showing fastener and o-ring detail;

FIG. 8 is a partial sectional view showing the extruded clip and stripgasket of an alternative embodiment; and

FIG. 9 is a schematic diagram of a solar hot water system.

DETAILED DESCRIPTION OF THE INVENTION

For the purposes of this description and for the claims following, theterm “o-ring” can mean both toroidal and flat-shaped, and connotescompressibility such that sealing is achieved. Similarly, the term“water” is to be construed as meaning any liquid.

A solar hot water heater 1 is shown in FIGS. 1 and 2. Solar hot waterheater 1 is comprised of a frame 2, which houses an absorber panel 10and a transparent cover 3, which provides an enclosure. The air space 5within the enclosure and above the absorber panel 10 functions to reduceconvective heat losses. Solar radiation 4, passing through thetransparent cover 3 and the air space 5, is incident upon the absorberpanel 10 where the radiation heats the contents therein by conductionthrough its absorption. Insulation material may optionally be addedbetween frame 2 and absorber panel 10. Coatings may also be optionallyadded to both the absorber panel 10 and the transparent cover 3 torespectively enhance absorption and decrease reflective losses. Such anapparatus is not only appropriate for residential use, but also forswimming pools and the general radiant heating of buildings.

The assembled absorber panel 10 is best shown in FIGS. 2 and 3. Absorberpanel 10 is comprised of absorber plate 11 and companion plate 12 joinedin a thinly-spaced-apart, sandwich-like, composite. Water is introducedto absorber panel 10 from a water supply 16 (not shown) through entryport 13, and is distributed from the absorber panel to a heat exchanger17 (FIG. 9) through exit port 14. Entry port 13 and exit port 14 can bepositioned either on the absorber plate or the companion plate. When theabsorber panel is mounted at an angle to vertical, such as when mountedon a pitched roof, exit port 14 should always be elevated above entryport 13 to vent air and prevent air bubbles.

In the preferred embodiment, absorber plate 11 and companion plate 12are comprised of a 48 inch by 96 inch by 0.032 inch aluminum sheet ofalloy 5052H32, or similar.

FIG. 4 shows the absorber panel 10 with the absorber plate 11 removed. Ameans for spacing 30 is shown at the periphery edges of the exposedcompanion plate 12, said means being a periphery gasket 32, and,preferably, an elastic gasket of rectangular cross-section 31. In analternate embodiment (FIGS. 6 and 7), periphery gasket 32 may be anelastic gasket of circular cross-section 34.

A means for channeling 40 is also shown in FIG. 4 extending fromalternating edges of periphery gasket 32, said means being a pluralityof elastic baffles of rectangular cross-section 33. Means for spacing 30and means for channeling 40 can be collectively described as a means forresiliently creating internal space and channels 100.

In the preferred embodiment, the elastic gasket of rectangularcross-section 31 is a butyl rubber or silicone strip measuring 5 mm by12 mm and having a durometer in the range of 55-70. The elastic bafflesof rectangular cross-section 33 may be of similar material and hardness,but reduced in size to 5 mm by 8 mm. In the alternative, the elasticgasket of circular cross-section 34 is cording of the composition ofbutyl rubber or silicone and measures one-quarter inch in diameter. Forsealing purposes, the rectangular cross-section has greater surfacecontact area. The circular cross-section, however, presents a uniformheight when the strip is twisted in conformance to contours.

Continuing with FIG. 4, periphery gasket 30 creates an internal space 15for the containment of water therein. Lengths of the elastic baffle ofrectangular cross-section 33, each length shorter than one of theperiphery edges to which it is placed in parallel and extendingalternately from the two periphery edges which are perpendicular to theafore-mentioned periphery edge, collectively form a system of channels43. Adjacent channels 43 are connected by alternating passages 42, thepassages being free spaces at the terminus of each wall section formedby the lengths of elastic baffle of rectangular cross-section 33. Thealternation of passages 42, from one perpendicular periphery edge to theother, creates a serpentine path 41 for the flow of water through theinternal space 15. FIG. 5 shows one of the channels 43 defined bybordering sections of elastic gasket of rectangular cross-section 31 andelastic baffle of rectangular cross-section 33, and particularlyillustrates the extreme low-aspect ratio of the channel; that is to say,the short depth to the wide breadth. Such an aspect ratio optimizes thecontact surface area for heat transfer.

In the preferred embodiment, a means for binding 20 comprises anextruded clip 23, as shown in FIG. 8. Extruded clip 23 extends aroundthe periphery of absorber panel 10 and overlaps the absorber plate 11and the companion plate 12 with clip arms 24. The corresponding meansfor spacing 30 is the elastic gasket of rectangular cross-section 31.Elastic gasket of rectangular cross-section 31 is positioned between theplates and between clip arms 24. Clip arms 24 stiffly angle toward eachother so as to form a narrowed opening 25. Clip arms 24 compress theelastic gasket of rectangular cross-section 31 there between to form awater-tight seal. The elastic gasket in envelopment by clip arms 24 andunder compression there from forms a wedge shape 35 in the interior ofextruded clip 23. The wedge shape 35 cannot pass the narrowed opening 25and thereby resists the removal of clip 23, thus securely holding it inplace. The extruded clip 23 may be removed by supplying a shear forcesufficient to effectively calender the wedge.

In an alternative embodiment, the means for fastening 20 comprisesmachine screws and nuts 21, as shown in FIGS. 6 and 7. In this case, thecorresponding means for spacing 30 is the elastic gasket of circularcross-section 34. Machine screws and nuts 21, shown in alternatingpositions on both sides of periphery gasket 30 in FIG. 6, serve both toanchor the gasket and to apply compressive force for sealing purposes.The staggered position applies the compressive force evenly around thegasket. The individually adjustable nature of each fastener makes itpossible to stop any leaks which may result from the variation ofmaterials and applied tension. In the same manner, machine screws andnuts 21 anchor the lengths of the elastic gasket of rectangularcross-section 31 forming the channels.

The machine screws and nuts 21 can also provide a means for shapingsurfaces and space. Because of the sheerness of the absorber andcompanion plates and the breadth of the channels, there will be bulgingof the plates when water is moving through the channels under pressure.Through-bolted machine screws placed at selected locations intermediatethe channels can be used to control the bulge, and moreover, to makeallowances for both heat and freezing expansions. All machine screwstraversing internal space 15 are provided with o-rings 22 to seal theperforations of that space. Because the machine screws and nuts 21 areeasily removable, it is a relatively simple matter to disassemble theabsorber panel for cleaning and maintenance. The machine screws ofpreference are one-half inch stainless steel, gauge 4-40. The o-ringsare 0.45 inches in diameter with a 0.21 inch thickness.

In another alternative embodiment, the heat exchanger 17 comprises thesame structural elements as absorber panel 10. In the case of heatexchanger 17, heated water is supplied through entry port 13 andcirculates to exit port 14. The heated water transfers heat by contactwith both absorber plate 11 and companion plate 12, thereby exchangingthe heat with any medium in contact with the plates.

In yet another alternative embodiment, a solar hot water system 50 iscomprised of at least one absorber panel 10 and at least one heatexchanger 17. Referring to FIG. 9, heat exchanger 17 is submerged in avolume of water 54 inside of a heat-exchange vessel 51. Heat-exchangevessel 51 might be a holding tank, or might also be a heat exchange tankfor a swimming pool heating system. A means for providing circular fluidcommunication 52 connects absorber panel 10 with heat exchanger 17through respective entry ports 13 and exit ports 14. A means forcreating a circulation current 53 transfers heat radiated onto absorberpanel 10 to heat exchanger 17, and there from, by conduction andconvection, to the volume of water 54. The means for providing circularfluid communication 52 may be plumping-supply piping or hose. The meansfor creating circulation current 53 may be a pump capable of operatingat low pressure.

The fabrication process for the absorber panel, and by extension, forthe heat exchanger, is simple. It requires laying out the baffles anddrilling a pattern of holes through the plates to anchor the baffles andto control bulge in the channels. With both plates in place and thegasket sandwiched between the periphery edges, the extruded clip ispressed onto and over the edges and against the resilient force of thegasket. In some cases, a mallet may be used to urge the extruded clipinto position. The holes are threaded with machine screws, o-rings andnuts, as appropriate. The entry and exit ports are mounted to one orboth plates.

The preferred absorber panel size is thirty-two square feet. Thepreferred size of the heat exchanger is twenty-five square feet.

It is to be understood that the invention is not limited in itsapplication to the details of construction and to the arrangements ofthe components set forth in the preceding description or illustrated inthe drawings. The invention is capable of other embodiments and of beingpracticed and carried out in various ways. For example, the elasticbaffles may be adhesively bonded in place thereby avoiding holes in theplates. Also, it is to be understood that the phraseology andterminology employed herein are for the purpose of the description andshould not be regarded as limiting.

1. A low-pressure absorber panel for solar hot water systems, comprising: an essentially rectangular aluminum absorber plate; an essentially matching aluminum companion plate in spaced relationship to the absorber plate to which it is joined below by a means for binding; a means for spacing to create an internal space between the absorber and companion plates for a flow of water there through, the means for spacing providing a water-tight seal; a means for channeling to create a serpentine flow path for the water; and at least one port through one of the absorber and companion plates for water to enter the internal space and at least one other port through one of the absorber and companion plates for water to exit, the at least two ports located so as to maximize the serpentine flow path, wherein the water flowing in contact with the absorber plate receiving solar radiation is heated by it and forms a medium for transferring heat.
 2. The low-pressure absorber panel of claim 1, wherein the means for spacing is an elastic gasket of substantially rectangular cross-section which is arrayed along the periphery edges of the absorber and companion plates and tensioned to provide a compression seal.
 3. The low-pressure absorber panel of claim 1, wherein the means for spacing is an elastic gasket of substantially circular cross-section which is arrayed along the periphery edges of the absorber and companion plates and adjustably tensioned to provide a compression seal.
 4. The low-pressure absorber panel of claim 2, wherein the means for binding is an extruded clip having arms angled so as to form a narrowed opening, the extruded clip covering the elastic gasket of substantially rectangular cross-section along the length of each periphery edge, the elastic gasket compressed between the arms to form a wedge shape which resists removal of the extruded clip from the periphery edge.
 5. The low-pressure absorber panel of claim 3, wherein the means for binding is machine screws and nuts straddling the gasket of substantially circular cross-section along the extent thereof, the machine screws optionally provided with o-ring seals for positioning in the internal space.
 6. The low-pressure absorber panel of claim 5, wherein the spacing of the machine screws is at sufficient interval as to prevent bulging of the plates under pressure.
 7. The low-pressure absorber panel of claim 1, wherein the means for channeling is a plurality of elastic baffles of substantially rectangular cross-section extending in alternation from one end or the other of the gasket at the periphery, beginning with the end closest to the entry port and ending with the end closest to the exit port, to a point short of the opposite end, whereby the parallel channels thereby formed are connected to adjacent channels by alternating passages, the elastic baffles held in place and in compression by bolts and nuts sealed with o-rings spaced along the length thereof.
 8. The low-pressure absorber panel of claim 1, further comprising a pressure differential of not more than 2 psi to urge the flow of water through the internal space.
 9. The low-pressure absorber panel of claim 1, further comprising a pressure differential of not more than 1 psi to urge the flow of water through the internal space
 10. The low-pressure absorber panel of claim 7, further comprising a means for volume expansion of not less than 9% to accommodate freezing water.
 11. The low-pressure absorber panel of claim 10, wherein the means for volume expansion is the loosening of screws and nuts interim the internal space to permit bulging therein.
 12. The low-pressure absorber panel of claim 1, wherein the rectangular aluminum absorber and companion plates each substantially measure 32 square feet.
 13. A low-pressure heat exchanger for hot water systems, comprising: an essentially rectangular aluminum absorber plate; an essentially matching aluminum companion plate in spaced relationship to the absorber plate to which it is joined below by a means for binding; a means for spacing to create an internal space between the absorber and companion plates for a flow of water there through, the means for spacing providing a water-tight seal; a means for channeling to create a serpentine flow path for the water; and at least one port through one of the absorber and companion plates for water to enter the internal space and at least one other port through one of the absorber and companion plates for water to exit, the at least two ports located so as to maximize the serpentine flow path, wherein the water flowing in contact with the absorber plate receiving solar radiation is heated by it and forms a medium for transferring heat.
 14. The low-pressure absorber panel of claim 13, wherein the means for spacing is an elastic gasket of substantially rectangular cross-section which is arrayed along the periphery edges of the absorber and companion plates and tensioned to provide a compression seal.
 15. The low-pressure absorber panel of claim 14, wherein the means for binding is an extruded clip having arms angled so as to form a narrowed opening, the extruded clip covering the elastic gasket of substantially rectangular cross-section along the length of each periphery edge, the elastic gasket compressed between the arms to form a wedge shape which resists removal of the extruded clip from the periphery edge.
 16. The low-pressure absorber panel of claim 13, wherein the means for channeling is a plurality of elastic baffles of substantially rectangular cross-section extending in alternation from one end or the other of the gasket at the periphery, beginning with the end closest to the entry port and ending with the end closest to the exit port, to a point short of the opposite end, whereby the parallel channels thereby formed are connected to adjacent channels by alternating passages, the elastic baffles held in place and in compression by bolts and nuts sealed with o-rings spaced along the length thereof.
 17. A low-pressure solar hot water system, comprising: a heat-exchange vessel containing a volume of water; at least one low-pressure absorber panel irradiated by the sun comprising an essentially rectangular aluminum absorber plate, an essentially matching aluminum companion plate in spaced relationship to the absorber plate to which it is joined below by a means for binding, a means for spacing to create an internal space between the absorber and companion plates for a flow of water there through, the means for spacing providing a water-tight seal, a means for channeling to create a serpentine flow path for the water; and at least one port through one of the absorber and companion plates for water to enter the internal space and at least one other port through one of the absorber and companion plates for water to exit, the at least two ports located so as to maximize the serpentine flow path, wherein the water flowing in contact with the absorber plate is heated by conduction and forms a medium for transferring heat; at least one low-pressure heat exchanger submerged in the heat-exchange vessel comprising a duplicate structure to that of the absorber panel, wherein heated water flowing in contact with the absorber and companion plates of the heat exchanger transfer heat by conduction there through to the volume of water; a means for providing a fluid communication loop between the at least one low-pressure absorber panel and the at least one low-pressure heat exchanger by connecting respective entrance and exit ports; and a means for creating a circulation current in the fluid communication loop to thereby transfer heat between the at least one low-pressure absorber panel and the at least one low-pressure heat exchanger.
 18. The low-pressure solar hot water system claim 17, wherein the means for spacing is an elastic gasket of substantially rectangular cross-section which is arrayed along the periphery edges of the absorber and companion plates and tensioned to provide a compression seal.
 19. The low-pressure solar hot water system of claim 18, wherein the means for binding is an extruded clip having arms angled so as to form a narrowed opening, the extruded clip covering the elastic gasket of substantially rectangular cross-section along the length of each periphery edge, the elastic gasket compressed between the arms to form a wedge shape which resists removal of the extruded clip from the periphery edge.
 20. The low-pressure solar hot water system of claim 17, wherein the means for channeling is a plurality of elastic baffles of substantially rectangular cross-section extending in alternation from one end or the other of the gasket at the periphery, beginning with the end closest to the entry port and ending with the end closest to the exit port, to a point short of the opposite end, whereby the parallel channels thereby formed are connected to adjacent channels by alternating passages, the elastic baffles held in place and in compression by bolts and nuts sealed with 0-rings spaced along the length thereof. 